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Short Battery Life

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Member

I am using a ---
Arduino Pro Mini 328 - 3.3V/8MHzhttps://www.sparkfun.com/products/11114
With a ---
SparkFun RFM69 Breakout (915MHz)https://www.sparkfun.com/products/12775
I am powering it with 4 AA batteries connected to the RAW input.
Under normal operation it should only transmit or receive about six times a day.
My batteries seem to have gone dead in two weeks or less.
I had the system in an outdoor electrical box which got quite wet inside
and blew one of my Arduino minis which I replaced.
Might this be the cause?
What should I expect for battery life?
Is there a better way?

User Extraordinaire

Also.. Both those devices run at 3.3v I'm sure they work down to 2.2v but alas the battery curve will be letting you down.

If you are using two by two 1.5 Alkaline / lithium to achieve 3v.. THEN!! A 1.5v battery is only1.5v for a short while... They spend most of their time at 1.1v so you will only have 2.2v to power your circuits...

If you are going to power these devices, make sure you A) Follow mike's advice and B) power from a 3.7v Lithium...

Super Moderator

As already mentioned, you need to design for low consumption - both hardware and software. You also need to MEASURE what it is, under 100uA is generally low enough to make most products viable (and the sort of figure that's aimed at commercially).

Here's a short list of things you MUST do:

1) Switch the power to the RFM69 using a I/O pin, so you can switch power to it only when you need to.

2) Place the processor in sleep mode when not transmitting.

3) Use a low power 32KHz oscillator as the sleep clock, PIC's have this capability build in - presumably an AVR does as well? PIC's use TMR1 for sleep, and you normally set it to generate an interrupt every second, and use that to run an RTCC which also sets the trigger for the next transmission. There doesn't appear to be any such crystal on the Pro Mini, so you might need to choose something else?.

4) Make sure nothing is using power that doesn't need to - such as the LED on the Pro Mini - remove it.

5) There's a link on the Pro Mini board to bypass the regulator for low power applications, the datasheet of the existing regulator doesn't tell you how much it wastes - you might be better using an external regulator, and bypassing that one. The ones I'm using only use 16uA quiescent current.

If it's any help, I'm looking for 5+ years battery life, and probably transmitting once a day - using a PIC, with no special precautions (no sleep), and transmitting every 5 minutes (for crude battery life testing) I got over 5000 transmissions, and this is via a GPRS modem. As the PIC wasn't going to sleep, that wasted 6.5Ah battery life - more than your AA's could even provide.

So it's vitally important to use sleep, and you'll probably need to change your processor to something more sleep friendly?.

Well-Known Member

Between transmissions you tell the transmitter to go into sleep mode - see datasheet. Plus you put the Arduino into sleep mode. You should end up using less than 0.5mA and hopefully much less(20uA). You will have to unsolder the power LED.

No idea, but I don't see the connection between 'low stock' and 'going out of business'?.

I've not looked at them, as I'm not interested in using a module, just a bare IC - and preferably a PIC

But as we've all told you, and as that website says, you MUST put the processor in sleep (and obviously must have some method of waking it up again when needed) - and as I also said, remove power to the transmitter as well.

Member

Between transmissions you tell the transmitter to go into sleep mode - see datasheet. Plus you put the Arduino into sleep mode. You should end up using less than 0.5mA and hopefully much less(20uA). You will have to unsolder the power LED.

I can't comment on Arduino, but on a PIC I use TMR1 to wake up every second to run the RTCC, and 'interrupt on change' to wake up from a switch change, and process the action. I know the Arduino has some interrupt input pins, and I presume they can be used to wake up from sleep?.

Well-Known Member

I read an article a couple of days ago about putting Arduinos to sleep and only waking on key change interrupt. With the power LED disconnected they were using just a few micro Amps. Alas, can't find the article now but it can be done.

Super Moderator

I read an article a couple of days ago about putting Arduinos to sleep and only waking on key change interrupt. With the power LED disconnected they were using just a few micro Amps. Alas, can't find the article now but it can be done.

I reconnected the power red LED since I only lifted one end of it and it is back to accepting uploads.
There is a green LED near pin 10 that is staying lit and sometimes it goes out. I do not think it should be doing that.

Member

I looked at it under my 4x magnifier and everything looks good.
No solder bridges, nada.
when I run my finger along the pins near pin 10 the green LED there goes out
and sometimes it goes out on its own.

Well, guess I'll have to order up another pro mini so it will be a while before I am back online.
Shucks. Just as I was having fun.